Organic photocatalysts composed of ubiquitous elements such as carbon and nitrogen have attracted attention as environment-friendly and resource-conscious materials. Graphitic carbon nitride (g-C3N4), which is a polymer that produces hydrogen through water photolysis (Non-Patent Literature 1), is a heterogeneous organic photocatalyst excellent in light resistance. A hydrogen production process in which fossil fuel is used as a starting material produces carbon dioxide in the production process. On the contrary, a hydrogen production process carried out through water photolysis by g-C3N4 produces no carbon dioxide. Such a process allows providing environment-friendly clean energy.
For example, g-C3N4 can be produced as a water-insoluble powdery polymer by consecutive polymerization of a monomer such as, for example, cyanamide (Non-Patent Literature 2), melamine (Non-Patent Literature 3), urea (Non-Patent Literature 4), thiourea (Non-Patent Literature 6), or dicyandiamide (Non-Patent Literature 5). Non-Patent Literature 7 discloses performing spin-coating with a solution of dicyandiamide and then heating the spin-coated dicyandiamide to obtain g-C3N4 in sheet form.